The present invention generally relates to natural gas measurement, and particularly relates to determining energy, based on BTU analysis, associated with natural gas flowing in a pipeline.
Pipeline delivery of natural gas requires accurate measurement of the volume of gas delivered to a given point in the distribution system. However, simply determining the volume of gas delivered over a given interval of time is inadequate for determining the economic value associated with that volume of gas. Because natural gas represents a source of energy, its real value depends on the amount of energy actually contained in a given volume of gas. The British Thermal Unit represents a common unit of measure for the amount of energy contained in natural gas. As natural gas typically varies between 900 and 1,200 BTU/ft3, the total amount of energy contained in a given volume of natural gas varies appreciably. Therefore, large-scale consumers and distributors of natural gas have an economic interest in determining the actual energy value of the natural gas used or transported by their facilities.
Several parameters are all necessary to accurately determine total volume and total energy associated with a gas flowing in a pipeline over a given interval of time, including temperature, pressure, supercompressibility, and BTU content. Existing natural gas measurement systems typically monitor a subset of these parameters and assume constant or defined values for the remaining parameters. BTU content, because of the complexity associated with its accurate determination, is typically not directly measured and energy content calculations use an assumed value. For significant volumes of natural gas, however, a fixed-value assumption for BTU content yields inaccuracies of appreciable economic value. Natural gas is itself comprised of a number of constituents and accurate determination of its BTU content requires identification of one or more of these key constituents. Simple calorimeter techniques are unsatisfactory for identifying the constituent makeup of the monitored gas flow. Gas chromatography offers superior analytical capability when compared to simple calorimeter techniques, at the expense of greater cost, size, and power. Indeed, present gas chromatograph systems adapted to measurement of natural gas BTU content are large, expensive, and require appreciable quantities of reference and carrier gases for analysis, resulting in significant maintenance requirements.
Accordingly, there remains a need for a small and inexpensive energy measurement system employing gas chromatography adapted for accurately determining the total energy and total volume associated with a natural gas flowing within a pipeline. The present invention addresses this need by advantageously employing a micro-miniature gas chromatograph for determination of natural gas BTU content. By further including the ability to directly monitor other critical flow parameters, the present invention provides an integrated apparatus for determining natural gas volume and energy measurement.
The present invention provides an energy measurement system for monitoring a natural gas flowing within a pipeline to accurately determine a total volume and total energy associated with the flowing gas over a given interval of time. By employing a micro-miniature gas chromatograph, the present invention accurately determines the BTU content of the monitored natural gas. By additionally monitoring other critical flow parameters of the natural gas, such as temperature, pressure, and flow rate, the present invention determines total volume and total energy delivered by the flowing natural gas. Employing micro-miniature technology, the gas chromatograph of the present invention has greatly reduced size and operating power requirements and uses only minute quantities of both carrier and reference gases. These characteristics of the micro-miniature gas chromatograph impart specific advantages to the overall system, such as the ability to operate from small solar panels or reduced capacity battery cells. Further, the minute quantities of carrier gas used, typically less than one micro-liter per BTU analysis, permit the use of gas canisters small enough to be integrated into the electronic enclosure. A further advantage of micro-miniature technology is the high level of integration that permits implementation of the gas chromatograph as a small, easily replaceable modular assembly.
The foregoing attributes combine to yield an energy analysis system providing small size, low operating power, and low consumption of consumable gases, resulting in a system suitable for remote, unattended installation with low maintenance requirements. Details and advantages of the present invention are made clear through explanatory text and by reference to drawings illustrating particular features of the system. Further although presented in the context of natural gas analysis, the present invention may be advantageously applied to many other fuel gas compositions.